Testosterone is a steroid hormone from the androgen group. In general, androgens promote protein synthesis and growth of those tissues with androgen receptors. Testosterone is anabolic, meaning it builds up bone and muscle mass. Testosterone has the following structural formula:

The original and primary use of testosterone is for the treatment of males who have too little or no natural endogenous testosterone production—males with hypogonadism. However, over the years, testosterone has also been given for many other conditions, e.g., reducing infertility, correcting lack of libido or erectile dysfunction, correcting osteoporosis, encouraging penile enlargement, encouraging height growth, encouraging bone marrow stimulation, reversing the effects of anemia and appetite stimulation.
There are several application methods for testosterone, including hypodermic injections and transdermal creams, gels and patches. However, hypodermic injections tend to be painful, inconvenient, and increase the risk of polycythemia. Transdermal creams, gels and patches are often expensive, cause acne and skin irritation at the site of administration, have poor compliance with daily administration, and fail to provide some patients with adequate testosterone levels.
Accordingly, an urgent need exists for methods of administering testosterone to provide benefits and improvements over conventional methods, e.g., hypodermic injections and transdermal creams, gels and patches, of administering testosterone to patients.